The present invention relates to a process for producing a water-soluble polymer. In further detail, the invention relates to a process for producing a 2-oxazoline group-containing water-soluble polymer useful as a crosslinking agent for an aqueous resin so that the residual amount of an addition-polymerizable oxazoline (which may be referred to as an oxazoline group-containing monomer or an oxazoline monomer) reduces. This invention also relates to a water-soluble polymer having both of the oxazoline group and a polyethylene glycol chain on the side chain.
In the radical polymerization, there have been known various kinds of processes to reduce the amount of residual monomers. In general, a process to remove residual monomers by vacuum distillation, steam distillation and so forth and a process comprising further addition of a polymerization initiator at the second half of a polymerization reaction have been known.
Also, as another process, a process to convert residual monomers into other chemical substances by a chemical reaction has been known. For example, there has been disclosed in U.S. Pat. No. 4,357,464 a process to reduce an amount of residual 2-isopropenyl-2-oxazoline by a reaction of the polymer solution with an acidic and nucleophilic compound such as sulfur dioxide gas, hydrogen sulfide gas, or sodium hydrogen sulfite and the like.
The removing process by distillation is limited to a monomer having a relatively low boiling point or being capable of azeotropically boiling with a solvent and it is hard to apply to a monomer having a high boiling point such as an addition-polymerizable oxazoline.
The process comprising further addition of a polymerization initiator as well as the process comprising reduction by a chemical reaction are not preferred because the processes leave impurities in the polymer solution, which affect badly on preservation stability and water resistance when the polymer is used as a part of coatings, adhesives and so forth.